Question

When gypsum is heated to 393 K, it forms

• A. $AnhydrousCaS{O}_4$
• B. $CaS{O}_4.0.5H_{2}O$
• C. $CaS{O}_4.5H_{2}O$
• D. Dead burnt plaster

Answer 1

The correct option is B $CaS{O}_4.0.5H_{2}O$

When gypsum is heated at 393 K, it loses its water of crystallization or all the water molecules and becomes calcium sulphate hemihydrate.

$CaS{O}_4.2H_{2}O\stackrel{393.K}{⟶}CaS{O}_4.\frac{1}{2}{H}_{2}O$